failure of storage containing another copy of oracle redo and archive logs

Hi,1. Could we keep multiple redo and archive logs on different storages attaced to hosts via SAN. 2. What would happen if any one location (storage) containing second archive nad redo logs is unavailaible. The main file system containing database and first copy of remain avialable. Would the database continue to work or will hang. Thanks in advance.

Re: failure of storage containing another copy of oracle redo and archive logs

Hi Jawed,

1- Yes you can and you must. Duplexing is recomended for redologs and archivelogs because a disk failure won't crash your database. Create at least 2 redolog groups with 2 logfile members, each in a different storage. Use log_archive_dest and log_archive_duplex_dest to define both archivelog destinations. If you need more help defining redolog groups and members don't hesitate.

2- The database will continue if you have log_archive_min_succeed_dest=1.

Re: failure of storage containing another copy of oracle redo and archive logs

hi,

Please note that if Oracle cannot write to a redo log file at any one time, that log file can no longer be trusted, and Oracle marks it as "STALE". This indicates that the log file cannot be relied upon to provide all the data written to the log.

In general, the stale status of a redo log member should not be a cause for great concern, unless you observe that this happens too frequently.

Note that, a stale log is not necessarily an invalid log, but more of an "in-doubt" one. Once the corresponding redo group becomes the current one again, the stale status will go away by itself.

Re: failure of storage containing another copy of oracle redo and archive logs

Thanks yoogeraj,

1. We have alocated some space from two separate storages devices on SAN to one server runing oracle. One strage has main file system for oracle database and its redo and archive files. Another secondary storage has a copy of redo logs and archive logs. Few days ago the secondary storage was unavaialble on SAN due to some fibre cable problem.2. We observed that oracle hanged due to missing path of secondary storage having another copy of redo log files.

I would like to know

a. Was it due to unavailibilty of secondary redo logs or something else.b. Is there any way or parameter to ensure that oracle will contiune to work even secondary stroage is abruplty removed or unavailable.

Re: failure of storage containing another copy of oracle redo and archive logs

Hi Eric,Yes we have control files duplexed as well,But I am unix administrator, So I don't access ORacle database.

My questions remains same. Could you give me a genral idea about my aforesaid questions. Does the duplexing of control files have any effect in availibilty of database if one location containing copies of redo and control files fails.

The above sql command added a group with 2 members. Thus, they are now multiplexed. You can just add members to existing groups as well.

MOST IMPORTANT:Make sure the members of the groups are on DIFFERENT physical devices -- because of otherwise, you would be defeating the purpose of multiplexing them in the first place (recovery from media failure)

hope this helps too!

kind regardsyogeeraj

No person was ever honoured for what he received. Honour has been the reward for what he gave (clavin coolidge)

Re: failure of storage containing another copy of oracle redo and archive logs

Hi Yogeeraj,Yes we did multiplexing of redo logs by putting them on differnet physical device. Even these physical devices are in different storage arrays.What I wanted to assure that in case of failure of one copy of redo log file the data base will not hang.

Re: failure of storage containing another copy of oracle redo and archive logs

Hi,

first of all: If you want to feel safe, test it yourself. So get yourself a testbox, install a second database just for you and may be your dba. Get a testversion for a windows-pc if nothing else is available, but you need to DO this kind of action, just to feel safe when it comes to the point where you HAVE to do it.

Kick away a redolog member and watch the alertlog what happens while you force logswitches. Bounce the DB while the log is defective. Replace the member with a valid one... Lot of things to find out, just to be confident you can handle it when it happens in production.

Allthough I did not a complete test since 8.0 I had some real defectives to fix in 8.1 and 9.2 and here goes....

Losing a redolog member will let the DB stay up and running. Been there, done that.

I only lost a controlfilecopy (one of three) once and that did crash the instance.Startup was impossible until I replaced the defective copy (I mind to remember that this was on release 8.0). I did not try to train that error out for some releases, so may be 9.x is doing diffrent.But I'll try this on my testdb next week, seems to be something that one should test once in a while :-)